To smoothly operate a mobile communication system, it is necessary to properly configure radio parameters of base stations such as the transmission power level of a common control channel. In a mobile communication system, a base station periodically transmits a common control channel to the entire cell and each mobile station is enabled to perform basic operations by receiving the common control channel. If the transmission power level of the common control channel is too low, the reception quality of the common control channel is reduced and the mobile station may not be able to operate properly. Meanwhile, if the transmission power level is too high, the common control channel causes interference with other cells. This in turn reduces the reception quality and prevents proper operations in other cells.
In conventional methods, the transmission power level of the common control channel is determined and set as follows:
(1) A desired reception quality level (represented, for example, by a bit error rate (BER), a frame error rate (FER), and/or a block error rate (BLER)) is defined and a degraded area percentage (area ratio) indicating the percentage of a portion of a service area where the reception quality is allowed to be below the desired reception quality level is defined.
(2) The probability distribution of geometry in the service area (distribution of probabilities of occurrence of geometry values) is obtained by a system-level simulation (simulation of the received power level under a multi-cell environment) based on an assumed maximum radio network load (maximum transmission power of all base station sectors), an assumed regular arrangement of cells, and assumed propagation losses (obtained taking into account random numbers representing the influence of shading caused, for example, by topography or buildings), and geometry values corresponding to the degraded area percentage are identified based on the probability distribution of geometry. Here, the geometry indicates values obtained by the following formula: total received power from selected base station/(total received power from other base stations+thermal noise power), and the selected base station indicates a base station with the lowest propagation loss at a given point.
(3) A link-level simulation is performed based on the geometry and an assumed multipath propagation delay and with the received power from other base stations approximated to the thermal noise. In the link-level simulation, minimum transmission power levels that are enough to satisfy the desired reception quality level at respective points associated with the geometry values corresponding to the degraded area percentage are obtained by gradually increasing the transmission power (the ratio in the maximum transmission power of the corresponding base station sector) of the common control channel.
(4) Based on the obtained results, the transmission power level of the common control channel is set in each actual base station manually by a network administrator.
The applicant was not able to find any published prior-art document related to the present invention before the filing date of the present application. Therefore, no prior-art document information is included in the specification.